1. Field of the Invention
The present invention relates to a variable shape mirror that is provided to an optical device such as an optical pickup device. In particular, the present invention relates to a variable shape mirror that is formed by using a bulk material having piezoelectric characteristics. In addition, the present invention relates to an optical pickup device having a variable shape mirror.
2. Description of Related Art
Conventionally, there are many reports concerning a variable shape mirror that can alter a shape of its specular surface, and there are roughly two types of variable shape mirrors as follows.
A first type is a variable shape mirror that is formed by laminating thin films. This type of variable shape mirror having a structure in which thin films are laminated is, for example, formed by laminating thin films in an order of a substrate, a lower electrode, a piezoelectric body, an upper electrode, an insulator, and a reflection film. In addition, as described in JP-A-2005-196859, for example, there is another type of variable shape mirror in which thin films are laminated on a substrate in an order of a lower electrode, a piezoelectric body, an upper electrode, and an elastic body, and the side of the substrate opposite to the side on which the thin film are laminated is made a circular cavity portion on which a reflection film is formed. Furthermore, the variable shape mirror that is formed as described in JP-A-2005-196859 can obtain a large shape change at low voltage because thickness of a film at a movable part can be made thin.
A second type is a type of variable shape mirror that does not use a piezoelectric body made up of a thin film but utilizes expansion and contraction in the vertical direction of a piezoelectric element made up of a bulk material so as to alter a shape of its specular surface. This type of variable shape mirror is made up of a mirror member having a shape like a thin film including a specular surface, a mirror support substrate for supporting the mirror member, a plurality of piezoelectric elements disposed between the mirror member and the mirror support substrate, and electrodes disposed so that a voltage can be applied to each of the piezoelectric elements as described in JP-A-2004-220702, for example.
However, the first type of variable shape mirror that is a type formed by laminating thin films may not have sufficient performance that is required to a variable shape mirror because that the piezoelectric body is a thin film and that piezoelectric characteristic of the piezoelectric body is inferior to the case of a bulk piezoelectric body. In addition, lamination of thin films for manufacturing the variable shape mirror requires a sophisticated manufacturing technique, so there may be problems of high manufacturing cost of the variable shape mirror and a heavy load on manufacturing works.
Furthermore, in a case of the second type of variable shape mirror, the plurality of piezoelectric elements disposed between the mirror member and the mirror support substrate require fine adjustment in a machining process of them so that each size of them matches or require to be cut out in a very small size. Therefore, there is a problem of an increase of manufacturing cost or the like because a loss of material is generated in a cutting process.